Owing to excellent heat resistance and other properties of silicone rubber, integrally molded parts of silicone rubber and metal have been used in a wide variety of applications including automotive parts such as gaskets, household parts such as fan frame seals, electric appliance parts such as water heater gaskets, and copier or printer parts such as fixing unit-related parts. In response to the currently growing application of silicone rubber to electric and electronic fields, there is a need for a primer capable of bonding silicone rubber having durable fatigue properties to members of gold, silver or the like typically used as electric contacts.
Heretofore, a number of primer compositions have been proposed as applicable to the adherends to which silicone rubber is to be attached. For example, JP-A 52-32030 describes a composition comprising a tetraorganotitanate, an epoxy group-containing alkoxysilane, an aliphatic unsaturation-bearing organosilicon compound, a platinum compound, a solvent-soluble polymer, and an organic solvent. JP-B 61-2107 corresponding to U.S. Pat. No. 4,332,844 describes a composition comprising an alkoxy group-containing organosilicon compound, an organotitanium compound, and a hydrosilyl group-containing organosilicon compound. JP-A 10-121023 discloses a primer composition comprising an organooxy group-containing organosilane compound and/or partial hydrolytic condensate thereof; a hydrosilyl group-containing organosilicon compound and/or an organosilicon compound having at least one hydrosilyl group and having 1 to 4 di- or trivalent, optionally substituted, aromatic rings per molecule or having an alkylene group of 2 to 30 carbon atoms; and an organoaluminum compound.
On use of these primer compositions, they firmly adhere to various plastics and ordinary metals such as iron and aluminum, but not to substrates having an inert surface such as silver and gold.